In conventional soldering operations, devices are individually soldered to one another by hand using a soldering iron. For example, in manufacturing diode bridges the diodes are laid into a holder and the individual crosspoints are then each hand soldered. This is quite time consuming since it requires four individual soldering operations for each diode bridge.
Hand-soldering diode bridges also generally give poor yields when used with unencapsulated diodes having leads soldered to the semiconductor diode chip. The reason for this is that the solder joint at the chip will frequently melt and open during the soldering of the leads. For example, a typical diode bridge has a 95% tin-5% lead solder joint at the chip and a 60% tin-40% lead solder for the leads. In this case, the solder at the chip joint has a melting temperature approximately 175.degree. higher than the solder at the leads. But the inability to accurately control the temperature imparted to the diode chip joint by the soldering iron frequently causes the solder at the chip to melt. This is especially a problem if the leads are small and good heat conductors or if the leads must be soldered close to the chip.
Recently, methods have been developed for soldering diode bridges by placing them into a plastic nest and inserting a solder preform at each of the four corners of the bridge. The bridge is then inserted into a hot air or condensation soldering oven to melt the solder preform at the corners. Although this technique is an improvement over the hand soldering method, it is still time consuming since four solder preforms must be carefully placed for each diode bridge, one preform for each corner. And the preforms must be so maintained prior to and during the melting of the preform.